Hydraulic drive systems are commonly used for large vehicles or stationary equipment. However, as the output speed increases at a given gear setting, the efficiency of the hydraulic drive is correspondingly reduced. This makes it inefficient to run hydraulic drives at the upper half of the gear setting. This problem may be overcome by having multiple gear settings, but the complexity of the resulting transmission negates the benefits of using a hydraulic drive.
An alternative to a hydraulic drive system is a mechanically driven system. However, conventional mechanical drive systems are limited to discrete gear ratios, which do not allow for infinite speed ratios as found in hydraulic drives. A great deal of power management between the engine and the transmission at all output speeds is necessary for transmission effectiveness. A purely mechanical drive is inadequate to ensure the efficient use of the engine's available power due to the discrete speed ratios, while a purely hydraulic drive has inherently poor efficiency at higher operational speeds.
With the increasing costs of fuel and more stringent emissions requirements, there is a need for more efficient drive systems for large and small vehicles, as well as stationary equipment, to replace traditional hydraulic and mechanical drive systems.
It is an object of this invention to provide a more efficient drive system for large and small vehicles and stationary equipment by combining hydraulic and mechanical power systems.
It is a further object of this invention to provide a transmission system for optimizing use of combined drive systems.
It is a still further object of this invention to provide a combined drive system with a dual or multiple speed, shift-on-the-fly gearbox for extended speed and torque ranges.
It is a still further object of this invention to provide an improved steering system for combined drive systems when applied to differential output speed requirements.